The present invention relates to a system for detecting a physical amount associated with the behavior or motion of an automotive vehicle, and a system for controlling vehicular behavior or motion on the basis of the detected physical amount associated with the vehicular behavior. More particularly, the invention relates to a system for detecting physical data, such as acceleration, speed, angular acceleration, force, torque and so forth at a selected point on the vehicle, and for controlling the physical amounts in order to realize a desired vehicular behavior or motion. Furthermore, the invention relates to a system which includes a reference model with predetermined response characteristics for controlling vehicular behavior to achieve the response characteristics of the reference model with monitoring of the physical amounts associated with the vehicular behavior.
As a typical model of behavior, the vehicular behavior of a vehicle body having steerable front wheels and rear wheels to be regarded as rigid, can be considered. Now, as shown in FIG. 1, a three dimensional coordinate system having x, y and z axes originated at the gravity center G of the vehicle body 1, is established. Regarding the vehicular behavior about the gravity center as rigid body motion within a three dimensional space, the vehicular behavior can be classified as six freedom motions, which include: (1) linear motion along the x axis - longitudinal motion, (2) motion along the y axis - lateral motion, (3) motion along the z axis - vertical motion, (4) rotational motion about the x axis - rolling motion, (5) rotational motion about the y axis - pitching motion, and (6) rotational motion about the z axis - yawing motion.
These motions are closely associated with vehicular driving characteristics. For example, yawing or rolling are important factors for determining vehicular driving stability. On the other hand, pitching and the vertical motion are caused by undulation of the road surface and/or acceleration and deceleration of the vehicle and are motions which affect the riding comfort of the vehicle.
In advanced automotive technology in recent years, active control technologies, such as anti-lock brakes, traction control, four wheel driving, four wheel steering, active suspension and so forth, for controlling vehicular characteristics as desired, have been developed and incorporated in modern vehicles. In such automotive control technologies, it is necessary to monitor vehicular behavior, particularly acceleration (angular acceleration), from time to time. For this purpose, a plurality of accelerations are often employed.
As a manner of monitoring vehicular behavior, JP-U-2-30780 (Japanese Unexamined Utility Model Publication) discloses a method for detecting a vehicular lateral acceleration and a yawing angular acceleration by employing two acceleration sensors mounted respectively at front and rear portions of the vehicle, and arithmetically processing the outputs from the sensors. In addition, for vehicular behavior control, the position of the gravity center of the vehicle, lateral slip angle at each wheel and wheel slippage are considered as important factors. The lateral slip angle is an angle derived on the basis of a ratio between longitudinal speed and lateral speed of the vehicle and influences the vehicular steering characteristics. On the other hand, the wheel slippage is a value derived by dividing a difference between the vehicular body speed and the rotational speed of a wheel by the vehicular body speed. It has been known that there is an optimal range of wheel slippage for most effectively transmitting engine driving force and braking force to a road surface. Among the active control technologies, there are some systems which optimally distribute engine driving force to four wheels in order to reduce the lateral slip angle toward zero, and some systems which control engine outputs and/or braking forces.
However, the vehicular behavior while traveling is typically a composite behavior of the above-mentioned six freedom motions. Therefore, for enabling monitoring of the vehicular behavior satisfactorily, at least six acceleration sensors become necessary. In addition, since the sensors per se are mounted on the vehicular body, which is in acceleration, the detected values have to be processed with respect to an acceleration coordinate system. Furthermore, the detecting direction of the sensor can rotate according to rotation of the vehicle with respect to the coordinate system of the road surface (static coordinate system). Therefore, correction by conversion of the coordinate system (for example, Eular's angular conversion) becomes necessary.
However, there is no prior art teaching which results in a solution for the above-mentioned problem and thus there is a limit to the precision of detection of the vehicular behavior. This can be an impediment to implementation for further advanced vehicle control technologies.
U.S. Pat. No. 4,829,434, issued on May 9, 1989, for "Adaptive Vehicle" discloses a system which detects "driving behavior" of the driver, "environmental conditions", such as weather, distances from adjacent vehicles, and "vehicle driving conditions", such as vehicular speed, acceleration by means of sensors, and performs total feedback control for the vehicle by establishing an intelligent base with respect to three basic conditions, i.e. the driving behavior, the environmental condition and the vehicle driving condition, by deriving an optimum condition based thereon.
The control as proposed in the above-mentioned United States Patent is intended to provide improved cornering criterion for the vehicle. Therefore, once lateral slip or spinning of the vehicle is initiated, this system will have no effect.
Here, in the theory of vehicular behavior, when a vehicle undergoes lateral slip or spinning exceeding a cornering criterion, the magnitude of the lateral slip and spinning can be reduced by reversing the steering toward the neutral position or beyond the neutral position (counter steering). On the other hand, when a substantial under-steering is caused to make it difficult to pass the corner, applying side braking for causing locking of the rear wheels (spin-turn) will assist in reducing the cornering radius. Such a counter steering technique and spin-turning technique are both highly advanced skills which are difficult to perform for the average driver. Namely, in the case of counter steering, it requires a lot of experience to exactly measure the required angle of steering in the reverse direction. Also, a spin-turn is a very difficult driving technique which can be done only by drivers who have advanced skill.